Method for preparing halogenated alkanes and alkenes

ABSTRACT

A method for preparing halogenated alkanes and alkenes which comprises reacting by contacting, for 0.005 to 0.1 seconds at a temperature of 675* to 850*C., a halogenating agent of the formula CC1xBr4 x, wherein x is an integer from 0 to 4, with a compound of the formula R2CH2, wherein each R is H, Cl or Br. The utilization of the above conditions prevents the formation of large amounts of undesirable tars.

United States Patent Mullin et a].

[ 1 Apr. 10, 1973 METHOD FOR PREPARDIG HALOGENATED ALKANES AND ALKENES Inventors: Charles R. Mullin; Donald J.

Perettie, both of Midland, Mich.

The Dow Chemical Company, Midland, Mich.

Filed: Mar. 13, 1969 Appl. No.: 807,116

Assignee:

US. Cl. ..260/654 R, 260/658 R Int. Cl ..C07c 21/04 Field of Search ..260/664, 654 R, 658 R,

References Cited UNITED STATES PATENTS 4/1961 Pitt et al. ..260/654 R 2,857,438 10/1958 Obrecht et al. ..260/658 R X Primary ExaminerLeon Zitver Assistant ExaminerJoseph A. Bosko AttomeyGriswold & Burdick, J. Roger Lochhead and C. E. Rehberg [5 7] ABSTRACT 1 Claim, No Drawings METHOD FOR PREPARING HALOGENATED ALKANES AND ALKENES BACKGROUND OF THE INVENTION US. Pat. No. 2,979,541 (Pitt et a1.) teaches the reaction of CCl CH,, at a temperature of 400 to 650C, for a residence time of 0.1 seconds to 20 seconds.

Said process produces low yields of useful chlorinated alkanes and alkenes, and produces large amounts of undesirable tars, i.e., hexachloroethane and other high boiling materials, which can clog the reactor and are difficult to separate from the desired product.

SUMMARY OF THE INVENTION The present invention is a method for preparing halogenated alkanes and alkenes which comprises reacting by contacting, for 0.005 to 0.1 seconds at a temperature of from about 675 to 850C, a halogenating agent of the formula CCl,Br, wherein x is an integer from to 4, with a compound of the formula R Cl-l wherein each R is H, Cl or Br.

The utilization of the above method results in high yields of valuable halogenated compounds without the usual undesirable side effect of the formation of large amounts of tar.

The halogenating agents contemplated by this invention are CCl,, CCl Br, CCl Br CClBr and CBr The compounds to be halogenated are C11,, CH Br, CH Cl, Cl-l Cl Cl-I Br and CI-l C1Br.

Compounds produced by the method of this invention include methyl chloride and bromide, vinylidene chloride and bromide, vinyl chloride and bromide, methylene chloride and bromide, trichloroethylene, tribromoethylene, chloroform, bromoform and ethylene dichloride and dibromide.

Temperatures of from 675 to 850C. are suitable for of CCl, CI'I CI, the mole ratio of CH CIICCL, is at least about 2 to 1, and more preferably about 3 to 1. 1n the reaction CG, Cl-l Cl, an inert diluent, such as N,,, may be added to increase the overall mole ratio of (CH,Cl+N )/CCl to about 10/1 to 100/1.

Pressure has not been found to be critical, and can suitably vary from subatmospheric to superatmospheric. Experimentation has also shown that the results of the reactions were independent of the material of construction of the reactor and the conditioning of same, i.e., smooth or rough interior walls.

SPECIFIC EMBODIMENTS EXAMPLE 1 CH was mixed with CCl and passed into a preheater (100 300C). The mixture was then passed into a Monel reactor (3 mm. [.D. by 21 inches long). The effluent was analyzed by vapor phase chromatography (V.P.C.). Less volatile products were trapped in a dry ice-methylene chloride trap, and also analyzed by V.P.C.

The temperatures reported in Table I below are accurate for approximately 90 percent of the length of the tube. The reactor temperature was monitored with thermocouples spaced 1 inch apart along the entire length of the reactor. Feed rates are given, and contact times were calculated by utilizing the volumetric flow rate in the reaction zone (total reactor volume) at the specific reaction temperature, assuming ideal gas conditions.

Conversion and product distribution are in mole percent. The product distributions quoted are calculated on the basis of one mole of CCl, reacted. The HCl present in the product is not calculated since other products account for its presence in an absolute sense.

CH4] Mole percent 0014 Dlluent Contact mole C014 feed CH4 feed feed time CO1:

Temp. C C.) ratio (cc./sec.) (cc./sec.) (cc./sec.) (see) couv. Tar (3112:0012 CHCl; CHJCI the method of this invention. For the reaction of CCl CH a temperature of 730 to 770C. is preferred, while for the reaction of CCl CH Cl, a temperature of 740 to 800C. is preferred.

Inert diluents, such as N argon, krypton or neon can be utilized. In the reaction of CCl, CI-I Cl, it has been found that by diluting the reactants with N in a mole ratio of about 10 to 1, the yields of Cl-ICl=CCl can be somewhat increased, with a resulting decrease in tar formation.

It is to be noted that excessive reaction times, i.e., above 0.1 second, greatly contribute to the formation of large amounts of undesirable tars. Therefore, it is important to observe the maximum contact times taught herein. Contact times ranging from about 0.005 to about 0.1 second are suitable. For the reaction of CCl CH a contact time of about 0.02 to 0.04 seconds is preferred, while for the reaction of CCl,: Cl-l Cl, a contact time of about 0.01 to 0.04 seconds is preferred.

In the reaction of CCl CH the mole ratio of Cl-L/CCl is preferably about 60 to 90/1; in the reaction Where material balance is lacking, cc1,=cc1, ac-

counts for the remainder.

EXAMPLE 2 CH Cl was mixed with CCl and passed into a preheater 100 to 300C). The mixture was then passed into a 2 foot long X 3 mm. ID. Monel capillary tube heated externally by a resistance tube furnace. The effluent was analyzed by the same techniques as 1 described in Example 1. 

